MessagePack\Packer::packMapHeader PHP Method

    private static function packMapHeader($size)
    {
        if ($size <= 0xf) {
            return \chr(0x80 | $size);
        }
        if ($size <= 0xffff) {
            return "Þ" . \chr($size >> 8) . \chr($size);
        }
        return \pack('CN', 0xdf, $size);
    }